1. Field of the Invention
The present invention relates to a printing plate, a method for making a printing plate, a reusing method for the printing plate, and a printing machine. More specifically, the present invention relates to methods for making and reusing a printing plate on which an image is written based on digital data, and a printing machine using such a printing plate.
2. Description of Related Art
Recently, in general printing methods, many printing steps have become digital. That is, image data are digitized by producing an image or text using, for instance, a personal computer, or by scanning an image using a scanner, and a printing plate is formed based directly on the digitized data. In this manner, printing workflow may be improved and the entire printing process may be abbreviated, and execution of high image quality has been facilitated.
A so-called PS plate (i.e., a presensitized plate) has been generally utilized as a plate in a conventional printing process. The PS plate usually includes a hydrophilic non-image area, which is made of anodized aluminum oxide, and a hydrophobic image area which is formed on the surface of the hydrophilic non-image area by curing a photosensitive resin. However, a plurality of steps is required for making a printing plate using the PS plate, and hence, it is expensive and time-consuming to make such a plate. Accordingly, it is not easy to shorten the time required for the overall printing process and to lower the cost thereof. This is one of the main factors increasing the cost of printed matter, particularly for short run printing. Also, a developing step in which a developer is used is required for cases where the PS plate is employed, and hence, it is not only a time-consuming process, but also creates a problem, from the viewpoint of preventing environmental pollution, in that developer waste must be treated.
Also, a method, in which a film containing punched out information of an original image is made to contact with a printing plate and is subjected to light exposure, is conventionally used for making the PS plate, and this production of the printing plate is one of the obstacles which prevents the formation of a plate directly from digital data and the digitalization of the printing process. Moreover, in a conventional method, a printing plate must be replaced with a new one after print job, and the used plate has been discarded.
There are some commercial methods which, in consideration for the above-mentioned disadvantage of using the PS plate, correspond to the digitized printing process and in which the developing process may be omitted. For instance, Japanese Unexamined Patent Application, First Publication, No. 63-102936 discloses a preparation method in which ink containing a photosensitive resin is used for a liquid ink jet printer to be injected onto a printing plate material and an image area formed by the ink is cured by a photo irradiation process. Also, Japanese Unexamined Patent Application, First Publication No. 11-254633 discloses a method in which a color offset printing plate is made using an ink jet head which discharges a solid ink.
Moreover, a method is known in which a printing plate is made by sequentially applying a laser absorbing layer made of carbon black and a silicone resin layer onto a PET (polyethylene terephthalate) film, and heating the laser absorbing layer by drawing an image using a laser beam so that the silicone resin is subjected to laser ablation. Another method is also known in which a printing plate is made by sequentially applying a lipophilic laser absorbing layer and a hydrophilic layer onto an aluminum plate and subjecting the hydrophilic layer to laser ablation in the same manner as above using the laser beam.
Further, a method has been proposed in which a hydrophilic polymer is used as a recording media and a plate is made by converting an irradiated part to be lipophilic by an optical imaging.
However, by applying the above-mentioned methods, although it may be possible to make a plate directly from digital data, the plate must be replaced with a new one, after print job, in order to start the next printing process, and hence, the used plate is also wasted in these methods.
Accordingly, an object of the invention is to provide a reusable printing plate and a method for making a reusable printing plate which may be directly imaged based on digital data and has a high image quality without chemical processing. Another object of the invention is to provide a method for reusing such a printing plate so that the plate may be used repeatedly. Yet another object of the invention is to provide a printing machine capable of using such a printing plate.
The present invention provides a printing plate, including a hydrophilic surface of a plate containing a photocatalyst; and a hydrophobic image area containing an organic compound which is present on at least a part of the hydrophilic surface, the organic compound being decomposed and removed by the irradiation of light having a higher energy than a band gap energy of the photocatalyst.
In accordance with another aspect of the invention, the photocatalyst is a titanium dioxide photocatalyst.
In yet another aspect of the invention, the hydrophobic image area is formed by discharging an ink type liquid containing the organic compound onto the hydrophilic surface of the printing plate using an ink-jet imaging device.
In yet another aspect of the invention, the hydrophobic image is formed by transferring an ink type material containing the organic compound onto the hydrophilic surface of the printing plate by using a film on which the ink type material containing the organic compound has been applied and a transfer device.
In yet another aspect of the invention, the organic compound is an organotitanium compound.
In yet another aspect of the invention, the organic compound is an organosilicone compound.
In yet another aspect of the invention, the organic compound is a fatty acid dextrin.
The present invention also provides a method for making a printing plate, including a step of forming a hydrophobic image area on at least a part of a hydrophilic surface of a plate containing a photocatalyst by using an organic compound which is decomposed and removed by the irradiation of light having a higher energy than a band gap energy of the photocatalyst.
According to the above method, it is possible to convert the plate surface to be hydrophilic by irradiating the plate surface with light having a higher energy than the band gap energy of the photocatalyst. This is due to the action that the photocatalyst per se is converted to be hydrophilic. The surface converted into hydrophilic functions as a non-image area to which a hydrophobic ink does not attach. A hydrophobic image is formed on the hydrophilic plate surface by using an organic compound, which may be decomposed by the action of the photocatalyst under the irradiation of light having a higher energy than the band gap energy of the photocatalyst, and used as an image area to which the hydrophobic ink is attached in order to exert the function as a printing plate.
Also, after the printing process is completed and ink on the plate surface is removed, the organic compound is decomposed by the action of the photocatalyst by the irradiation of light having a higher energy than the band gap energy of the photocatalyst onto the surface so that the plate surface is converted to be hydrophilic. Accordingly, it becomes possible to recover the plate to a state prior to the formation of the image area thereof.
In accordance with another aspect of the invention, the photocatalyst used in the above method for making a printing plate is a titanium dioxide photocatalyst.
In yet another aspect of the invention, the hydrophobic image area is formed by discharging an ink type liquid containing the organic compound onto the hydrophilic surface of the plate using an ink-jet imaging device.
In yet another aspect of the invention, the hydrophobic image area is formed by transferring an ink type material containing the organic compound onto the hydrophilic surface of the plate by using a film (e.g., a thermal transfer ribbon) on which the ink type material containing the organic compound has been applied and a transfer device.
In yet another aspect of the invention, the organic compound used in the above method is an organotitanium compound.
In yet another aspect of the invention, the organic compound used in the above method is an organosilicone compound.
In yet another aspect of the invention, the organic compound used in the above method is a fatty acid dextrin.
The present invention also provides a reusing method for a printing plate made by using a method described above, including the steps of removing ink from the surface of the printing plate after the completion of a printing process; and reusing the printing plate by converting the surface of the printing plate so as to be hydrophilic by decomposing and removing a hydrophobic image area on the printing plate by the irradiation of light having a higher energy than the band gap energy of a photocatalyst onto the surface of the printing plate.
According to the above reusing method, since the plate surface is readily regenerated by irradiating light having a higher energy than the band gap energy of the photocatalyst, time and cost required for the regeneration process of the plate can be significantly and effectively reduced.
The present invention also provides a printing machine including a print drum which is provided with a hydrophilic plate surface containing a photocatalyst; a plate cleaner which removes ink on the plate surface; a light irradiation device which irradiates light having a higher energy than the band gap energy of the photocatalyst onto the plate surface; an image formation device which forms a hydrophobic image area on at least a part of the plate surface by using an organic compound which is decomposed and removed by the irradiation of light having a higher energy than the band gap energy of the photocatalyst; and a dryer which dries the plate surface.
According to the above printing machine, the production and regeneration process of the plate may be carried out by using the printing machine.
In accordance with another aspect of the invention, the light irradiation device, the image formation device, and the dryer are disposed in that order around the print drum with respect to the direction of rotation of the print drum.
According to the above printing machine, the production and regeneration process of the plate may be performed continuously in association with the rotation of the print drum.
In yet another aspect of the invention, the photocatalyst used in the above printing machine is a titanium dioxide photocatalyst.
In yet another aspect of the invention, the image forming device is provided with an ink jet head, which discharges and ink type liquid containing the organic compound and forms the hydrophobic image area on the hydrophilic plate surface.
In yet another aspect of the invention, the image forming device is provided with a film on which the ink type material containing the organic compound has been applied and a transfer device which transfers the ink type material containing the organic compound onto the hydrophilic plate surface from the film, and forms the hydrophobic image area on the hydrophilic plate surface.
In yet another aspect of the invention, the organic compound used by the image formation device is an organotitanium compound.
In yet another aspect of the invention, the organic compound used by the image formation device is an organosilicone compound.
In yet another aspect of the invention, the organic compound used by the image formation device is a fatty acid dextrin.